It is proposed to study the development of the magnocellular and parvicellulare neurosecretory systems in the guinea pig by means of light microscopic immunocytochemical demonstration of neurophysin and luteinizing-hormone releasing factor (LRF), respectively, combined with a classical electron microscopic study of the developing median eminence. These experiments are designed to detail the morphological and biochemical events in the embryo, neonate, and prepubertal animal which result in maturity of the hypothalamo-pituitary axis. Experiments to localize LRF in the hypothalamus of the adult rhesus monkey will also be conducted. Electron microscopic immunocytochemical localization of LRF and neurophysin in both guinea pig and monkey hypothalamus will establish: (1) their subcellular distribution; (2) their time course of release during different physiological and experimental reproductive states and (3) the contribution of both neuronal and ependymal elements of the median eminence to the delivery of hypothalamic hormones to the primary portal plexus and thus to the anterior pituitary.